Automatic chemical analyzers capable of analyzing a biochemical sample, such as blood or urine, in terms of plural items have been already proposed. For example, an automatic chemical analyzer described in Japanese Patent Laid-Open No. 2024/1993 comprises a sample disk holding a plurality of sample containers, a reaction disk holding a plurality of reaction containers, and a plurality of reagent disks holding a plurality of reagent containers. In this instrument, aliquots of sample in the sample containers set on the sample disk are drawn in by a pipetting mechanism and dispensed into the reaction containers on the reaction disks. Another pipetting mechanism draws in reagents from plural reagent disks and feeds the reagents into reaction containers. Thus, the sample is chemically analyzed in terms of various items in each reaction container.
The sample and the reagent are held in their respective containers. Predetermined amounts of these sample and reagent are taken from the containers by pipettes and dispensed into the reaction containers. The volume of liquid that the instrument can meter out has a limitation. For example, the liquid mass around the tip of a pipette breaks at a location that is not fixed. Therefore, in the prior art technique, the minimum amount of liquid that can be metered with sufficient reproducibility is about 3 .mu.l.
Generally, in a chemical analyzer, the amounts of a sample and a reagent put into a reaction container are set to a ratio of 100:1, taking account of the dynamic range of the induced chemical reaction. Since reagents are expensive, it is desired to minimize the amounts of reagents used. Accordingly, it may be considered to reduce the amount of sample subjected to a reaction. However, because of the limitation described above, it is impossible to reduce the amount of sample below about 3 .mu.l at present.